Data from the study, led by Prof Ephraim Fischbach and Prof Jere Jenkins of Purdue University, suggest that the rate of breakdown of radioactive materials changes in advance of solar flares.

They hope they can use this to develop a system that could predict when a potentially devastating geomagnetic storm might take place. This would allow authorities to adopt protective measures, such as shutting down satellites, at times of most risk.

But it is unclear how long such a system would take to develop. Prof Jenkins told BBC News: "We're still developing algorithms to pinpoint what type of flare and magnitude it will be."

Other physicists are more sceptical. Dr Peter Sole, a particle physicist at the University of Glasgow, commented: "The variation in the decay rate of different radioactive isotopes seems to be real." However, he thought that environmental effects, such as tempertature or humidity, might have affected instruments used to measure this.

He also thought cosmic ray variations could be the culprit - by inadvertently interacting with a key component of the instrument used to measure the radioactive decay. Dr Soler argued that "they should do similar experiments underground, where the cosmic ray rate is reduced dramatically to rule out such effects".